Plastic containers having one-piece, integral construction, including the cover, are known. Typically, an area of reduced wall thickness is made between the cover and the container neck. The cover is removed by rotating a threaded neck ring which exerts an axial force, either in compression or tension, on the cover and fractures the area of reduced wall thickness.
Although containers of this type have found application in the medical industry, e.g., for storing and dispensing sterile liquids, on occasion a minute amount of liquid sometimes spills onto the outer surface of the container during opening. This is the result of small amounts of the liquid accumulating in the area of reduced wall thickness. This may occur, for example, during shipping or handling, via splashing or sloshing, or tilting of the container. When this area is fractured during opening, the liquid may escape onto the exterior surface of the container, typically onto the neck threads. Although the medical significance of such small amounts of liquid on the container threads is subject to debate, it is generally recognized as being commercially undesirable.
This problem has been solved by the invention disclosed in above-identified U.S. Pat. No. 4,478,342, incorporated by reference herein. As shown in that patent, the container includes body, neck and cover portions of a one-piece plastic construction. The line of weakness is defined between the neck and cover portions to permit selective separation of the cover portion from the neck portion. A separately formed inner closure member is provided in the container, which inner closure is carried by the cover and isolates the container contents below the frangible line of weakness. The inner closure serves as a liquid seal of the container contents from the line of weakness so that when the container is opened by breaking the frangible line of weakness, the inner closure is removed with the cover and liquid will not escape onto the exterior surface of the container.
The nesting engagement between the inner closure and the neck portion provides a liquid-tight seal between the inner closure and the neck while permitting easy withdrawal of the inner closure with removal of the cover. Where circumstances permit, e.g., where sterility of the contents is not required, the nesting arrangement also permits resealing of the container in the event all of the contents are not used.
In medical applications, the contents of the container shown in U.S. Pat. No. 4,478,342 is typically sterilized by the application of heat sufficient to destroy germs and microbes which would otherwise make the container contents medically unacceptable. After heat sterilization, the exterior of the container is typically splashed with water such as from shower-type spraying nozzles. This drastically reduces the cooling time of the containers, which therefore also drastically reduces the time for the plastic, perhaps as hot as 250.degree. F. upon heating, to set, and enables earlier handling by equipment or people at a subsequent work station. Thus, the decreased cooling cycle time caused by the water spray greatly increases the speed by which the containers may be manufactured, thereby improving efficiency.
Heat sterilization presented a new problem with this improved container with the cover-removable closure. During the cooling step, it was found in some instances that the cover of the container had a tendency to collapse. Such collapse is highly undesirable for a number of reasons. The collapse of the cover may make subsequent installation and operation of the threaded neck ring on the cover impossible. The collapse of the cover may create additional stress on the preformed line of weakness sufficient to destroy the effectiveness of the container as a sterile barrier to the container contents at the line of weakness. The added stress may be sufficient to actually break the line of weakness. Additionally, the collapsed cover has a misshapen appearance which makes the container commercially unacceptable.
The problem of cover collapse in the container has been solved in U.S. Pat. No. 4,478,342 by providing moist air in the chamber defined between the cover portion and the inner closure, while still preventing moisture in the defined chamber from dripping out of the defined chamber onto the exterior surface of the container upon the opening thereof.
In one embodiment shown in that patent, the defined chamber is closed to chamber-external moisture. A small volume of liquid is carried in the defined chamber, segregated from the defined volume. The liquid is dispensed into the inner closure before the formation of the cover and the chamber defined by both the cover and the inner closure.
In another version, the defined chamber is not closed. Instead, a vent is provided. The vent is disposed between the chamber and the defined volume of the container and includes an opening in the inner closure in communication with the defined volume of the container. The opening is small enough to prevent moisture in the defined chamber from dripping therethrough.
When the first alternative is chosen, i.e., when the defined chamber is closed to chamber-external moisture, including the contents of the container below the inner closure, a small volume of liquid must be added to the defined chamber in a separate operation. Typically, this is performed by placing a drop of liquid in the inner closure before the inner closure is inserted into the blow mold. This necessitates use of machinery for providing a separate source of clean, if not sterile, liquid; providing means for metering the liquid into the inner closure before the blow molding operation; and ensuring that none of the liquid placed in the inner closures spills out of the inner closure, into the parison below the to-be-formed frangible line of weakness for example, thereby mixing with the container contents. Also, the bottom surface of the inner closure is typically tapered so that liquid will not adhere to the outside thereof. With the bottom tapered surface, the inner closure does not sit squarely on a flat surface. This aggravates the problem of ensuring that liquid placed in the inner closure stays within the inner closure during tranfer of the inner closure to the blow mold.
The second alternative, i.e., providing a vent opening in the inner closure, does not require the addition of liquid into the inner closure before blow molding. The vent opening allows moist air to enter the defined chamber from the container contents below the frangible line of weakness during heat sterilization. The opening is designed to be small enough to prevent moisture which has entered the defined chamber during sterilization from exiting the defined chamber through the vent opening. As disclosed in U.S. Pat. No. 4,478,342, moisture could otherwise exit the defined chamber during opening of the container, thereby possibly dripping onto the non-sterile, external container threads, which would thereby defeat one of the principal purposes of the inner closure.
Typically the container, including the cover portion thereof, is made of an optically translucent or transparent plastic so as to allow for visual inspection of the container contents. Such a construction also permits viewing of the moisture trapped in the defined chamber during sterilization because of the vent opening however and it has been found that such an arrangement may be commercially undesirable, raising questions in the minds of medical personnel as to the reasons for the moisture in the upper defined chamber, even though the moisture trapped through the vent opening is sterile and is the same liquid as the container contents. Moisture is also visible in the defined chamber with the earlier described alternative in which moisture is added into the closure in a separate operation.
Such containers also are difficult to test for improperly made containers using standard test procedures. It is desirable to test the integrity of the frangible line of weakness during the manufacturing operation so as to reject those containers which leak at the line of weakness. With either embodiment shown in U.S. Pat. No. 4,478,342, additional moisture from the container contents cannot be forced into the defined chamber or adjacent the line of weakness under pressure and thus it is difficult to check for improperly made containers.